The
Trafictec CMU Conflict Monitor Unit, which is
optional for use with the SBC-2400 Traffic Control
System, monitors selected traffic
signal controller channels for conflicts. There are
8 input lines and 6 CMU channels. Two sets of input
lines are tied together, forming a single signal
group (i.e., Green and Walk) that can be monitored
as one channel. When two channels are in conflict,
the CMU will activate a conflict signal. This signal
is read by the traffic controller, which will then
place the intersection in flash. The conflict signal
is latched and can only be cleared by a manual
reset. The latching relay maintains the fault status
during a power outage.

Front panel LEDs illuminate when a channel is
active. A small super capacitor is used to power the
LED latch and will maintain the information for
about 2 hours. After this period, the front panel
LEDs may not show the correct information, but the
latching relay will stay in the fault state until
manually reset.

The
CMU channel inputs can be one of three types (12
VDC, 110 VAC or 220 VAC) and must be selected at the
time of order. The CMU is powered by a 12 VDC power
supply in the traffic cabinet.

Clean,
Single-Board Design

All
channel inputs and power enter the CMU via a front
panel DB15P connector. The +12 VDC power passes
through a diode, and a 100 µF
capacitor acts as an input filter. All circuitry,
including the supercap recharging circuit, is
powered by 12 VDC. There are no other power
supplies in the CMU.

The
channel inputs pass through a pre-selected resistor
based on the signal voltage. The signal then drives
an opto-isolator and then back to the channel return
pin. The output side of the opto-isolator is pulled
up by a 47 kohm resistor. When the input is On, the
output is driven low to ground.

The
channel signal then enters a NOR gate matrix, where
each CMU input channel is OR'ed with the other input
channels. Both inputs being low will invert the
output signal and cause the high state to enter a
series of DIP switches. These are used to select
which channels are monitored for conflicts. The user
turns on each switch to select pairs of input
channels which should never be both on at the same
time, or a conflict will be detected. There are 15
DIP switches in two banks of 8. The last switch is
not used.

Two conflict signal branching circuits are at
the exit of the DIP switches:

Circuit one is the front panel LED latch. The
conflict status of the channels is shown by LEDs on
the front panel, and this information is latched
following a conflict so the technician can see what
channels caused the fault. The LED latch driver has
a small super capacitor to save data for about 2
hours. If the power is interrupted for a longer
period, the LED data may not be valid.

Circuit two is the conflict signal, which is
branched to the delay timer/ latching relay driver.
Because a slight residual voltage may exist on the
channel input after the controller turns off the
signal output, a 450 ms delay allows all CMU
channels to stabilize and not give false conflicts.
If the conflict is present for longer than this
delay, the latching relay is driven active and can
only be reset by a manual pushbutton on the CMU
front panel.